Ricinoleate derived urethane adhesives that cure by reaction of the isocyanate groups with compositions having reactive hydrogens such as water, amines, urethanes, ureas, polyols and the like are well-known in the art. While these adhesives exhibit excellent adhesion, water resistance and flexibility after curing, they are deficient in green strength before curing for many applications. "Green strength" as used herein means the ability to hold two surfaces together when first contacted and before the adhesive develops its ultimate bonding properties when fully cured.
The degree of green strength exhibited by an adhesive is vital to many applications. High green strength tends to prevent wrinkling and slippage of films during laminations. In panel assembly and packaging it permits faster handling and wrapping. When adhesive is applied to a vertical surface, a sufficiently high green strength prevents a mechanically unsupported, bonded member from slipping under the influence of gravity. When employed for flocking, high green strength holds the fibers in place while the adhesive cures and in the laying of carpet or synthetic flooring, it resists curling due to the shape memory thereof acquired when stored in a roll.
Attempts to increase the green strength of isocyanate terminated ricinoleate prepolymers by adding other high polymers such as polyvinyl acetate, cellulose acetate butyrate, acrylics, polyketones, phenoxy and polyvinylchloride-vinyl acetate copolymers have proven unsuccessful.
Chlorinated polyvinyl chloride (CPVC) is known for its excellent adhesion to rigid polyvinyl chloride and other rigid plastics, high tensile strength and inherent flexibility but not as a product known to impart green strength in adhesives as claimed in the present invention.
In accordance with the present invention, the use of chlorinated polyvinyl chloride with an isocyanate terminated ricinoleate prepolymer produces new and unexpected results including coverting the prepolymer from one that has little tack to one that is tenacious. Since the tenacity occurs before the composition cures, it is referred to as green strength. Additionally, the aforesaid prepolymers with chlorinated polyvinyl chloride exhibit the quick grab properties of contact type adhesives when applied to only one substrate instead of both, improved adhesion to certain substrates, improved water resistance and hydrolytic stability and improved film forming properties.
The aforesaid advantages are achieved only with a ricinoleate derived prepolymer, the increase in green strength not being noted when using prepolymers not derived from ricinoleate polyols. Such non-ricinoleate derived prepolymers are either incompatible with chlorinated polyvinyl chloride or, when compatible, exhibit quicker tack-free dry without improved green strength.
While high green strength makes the compositions of this invention particularly well suited for adhesives, the compositions also have utility as a coating. Isocyanate terminated urethanes that cure are often used interchangeably as both coatings and adhesives. A coating can be looked upon as a one-substrate adhesive and an adhesive as a two-sided coating. The preferred type of urethane sealers, primers and topcoats for floors are those which develop sufficient hardness quickly so that they can accept traffic. This minimizes shutdown time whether it be a new construction site or an operating office, factory and other site. As used herein, the term "adhesive" is intended to include such coatings or other uses to which the claimed compositions may be put.